An excellent entry, with a fun-to-play-with mechanic and absolutely lovely sprites (as I am typing, I look at the gif you made and I am still amazed at them). I would love to see the ays you could expand on it. By the way, did the elements affect the enemies in different ways? On the three types I tested upon, I could not see an obvious difference...

I feel like the parallax scrolling is really not appropriate here because we are relying on elements on that same layer (the element charging points). It makes the traversal somewhat confusing when judging distances.

Very fun game. Nice title screen, the character animations look smooth (that knight is awesome), fire and water effects look great. Each enemy offers enough variety to be conquered differently. The music stops after a fixed amount of time and SFX would be a nice touch. Overall, great job!